Variable orifice for multistage flash evaporation or distillation units

ABSTRACT

In a multistage flash unit, the interstage partitions terminate above the flowing distilland, and a flexible or hinged flap is connected to the bottom of each partition. The free end of each flap extends downward and is held in contact with flowing distilland by means of a weight or spring. If the force of the spring or weight just counterbalances the interstage pressure differential, the flap maintains wiping, surface contact with the distilland, and offers negligible resistance to flow. If the force of the spring or weight is greater than the interstage pressure differential, the flap dips into the distilland and acts as a flow control valve.

tlnited States Patent [72] Inventor Roscoe Van Winkle Knoxville, Tenn.

[21] Appl. No. 29,946

[22] Filed Apr. 20, 1970 [45] Patented Jan. 11, 1972 [73] Assignee The United States of America as represented by the Secretary of the Interior [54] VARIABLE ORIFICE FOR MULTISTAGE FLASH EVAPORATION OR DlSTlLLATlON UNITS [50] Field of Search... 202/173, 174, 236, 235; 203/10, 1 1, 88; 159/2 MS [56] References Cited UNITED STATES PATENTS 3,336,966 8/1967 Goeldner 159/2 MS 3,172,824 3/1965 Mulford 203/11 X Primary ExaminerNorman Yudkoff Assistant Examiner- David Edwards Alt0rneys--Ernest S. Cohen and M. Howard Silverstein ABSTRACT: ln a multistage flash unit, the interstage partitions terminate above the flowing distilland, and a flexible or hinged flap is connected to the bottom of each partition. The free end of each flap extends downward and is held in contact with flowing distilland by means of a weight or spring. If the force of the spring or weight just counterbalances the interstage pressure differential, the flap maintains wiping, surface contact with the distilland, and offers negligible resistance to flow. [f the force of the spring or weight is greater than the interstage pressure differential, the flap dips into the distilland and acts as a flow control valve.

DISTILLAND FLOW Ice VARIABLE ORIFICE FOR MULTISTAGE' FLASII EVAPORATION OR DISTILLATION UNITS The invention relates to interstage vapor seals in flash evaporation or distillation units, and more particularly to a variable interstage orifice which automatically compensates for variations in levels of fluids flowing in such units. This invention was made in the course of, or under, a contract with the United States Atomic Energy Commission.

In the prior art, a series of wires and/or elaborate orifice controls have been employed to maintain the pressure differential between stages, and to control distilland flow through a generally horizontal multistage flush unit, so as to prevent blow through or backup of liquid in any one stage. It can be seen that adjustment of such serially arranged orifices in a difficult task. This adjustment or tuning is particularly difficult if very shallow fluid flows are utilized to maximize flashing efficiencies and if interstage differential pressures vary from stage-to-stage. Furthermore, these weirs or orifices may be ineffective if flow conditions vary during operation of the flash evaporation or distillation unit.

I have now developed a simplified means for controlling fluid flow between stages. Generally, the device consists of a vapor-impermeable, flexible or hinged flap employed as part of each interstage partition within the shell of a multistage flash unit. The top of the flap is pivotally secured to a part of the shell structure such as the bottom of an interstage wall or partition projecting part way down from the shells ceiling and terminating above the flowing distilland. A force is applied to the flap which opposes the interstage pressure differential so as to hold the bottom portion of the flap in contact with the distilland flowing between stages. This force may be produced, for example, by attaching a weight or a spring near the free end of the flap.

If the force applied to the flap just counterbalances the interstage pressure differential, the flap wipes the surface of the distilland and offers negligible resistance to distilland flow and has essentially no effect on the interstage flow rate. When changes in the flow rate are brought about, for example, by changes in flow to the system, the flap simply raises or lowers in response to raising or lowering of the distilland level. In this manner of operation, the flap acts only as a pressure seal and as a self adjustable orifice, and not as a liquid flow control means. A multistage flash unit employing such a flow system is described in copending patent application Ser. No. 1 1,224.

If the force applied to the flap is significantly greater than the interstage pressure differential, the flap dips down into the distilland and acts as a flow-regulating device.

It is one object of the invention therefore to provide a pressure seal and self-adjustable orifice between stages of a multistage flash unit, which orifice does not hinder flow of distilland between flash evaporation stages.

A further object is to provide a simplified distilland flow control means.

Other objects and advantages will be obvious from the following more detailed description of the invention in conjunction with the drawings in which:

FIG. 1 is a fragmentary, cross sectional view of one embodiment of the present invention; and

FIGS. 2-4 are alternative embodiments.

Referring to FIG. 1, therein is shown two adjacent evaporator stages A and B in a multistage flash evaporation or distillation unit 1. A rigid wall 2 projecting part-way from ceiling 3 toward floor 4 of unit 1 effects a partial separation between stages A and B. Flow of distilland 5 (e.g., heated sea water) is from higher pressure stage A to lower pressure stage B. Reference numeral 6 designates transverse flap means connected to the bottom of wall 2.

In this embodiment, flap 6 is fabricated of flexible material such as neoprene, rubber or plastic. A weight 7 attached to the downstream face of flap 6 just counterbalances the interstage pressure differential so that flap 6 wipes or floats on the surface of distilland 5 and offers negligible resistance to flow,

where b the flap acts only as a ressure seal. Any convenient materla such as a stainless steel ar or rod can be employed as the weight 7.

In some stages, the interstage differential pressure may exceed the force that can readily be supplied by the weight attached to the flap. Accordingly, as shown in FIG. '2, a spring 8 is used instead of the weight to hold the flap 6 in wiping contact with the flowing distilland 5. A leaf spring attached to the flap, or molded therein, would also accomplish the same result as the coil spring 8. Such springs would provide suitable force for large interstage differential pressures, e.g., 60 inches of water. As stated above, these embodiments of the flap can be employed in the system described in copending patent application Ser. No. I 1,224.

Referring now to FIG. 3, the flap therein, designated as 6a, is fabricated from a rigid material and is pivotally connected to wall 2 by hinge 9. A weight or spring (not shown) can be employed to maintain contact between the rigid flap and flowing distilland. A flexible barrier 10 may be used to prevent vapor leakage through hinge 9. Although not illustrated, the rigid flap 6a may preferably have a hydrofoil shape on the upstream side thereof to improve flow therepast under all flow conditions.

In FIG. 4, the flap 6 is shown submerged in flowing distilland 5. This is brought about by employing a weight 7a which exerts a force greater than the interstage pressure differential. In this manner flap 6 controls the flow rate between chambers in the manner of prior art interstage orifices. Weight 7a can be chosen to effect predetermined flow rates. A spring (not shown) to apply appropriate force may be used to replace the weight 7a to control flow.

It will be apparent that a combination of weights and springs may be used to achieve automatic control similar to that obtained with the above described embodiments in specific applications. Furthermore, the forces may be applied only near the bottom of the flap, as shown in FIGS. 1, 3 and 4 or may be distributed along the flap. Also, the rigid flap may have sufficient mass so as to eliminate the need for a separate weight or spring to supply the required force to equal or exceed the interstage differential pressure.

What is claimed is:

1. A device for controlling the generally horizontal flow of fluids between adjacent, generally horizontal flash evaporator stages, wherein distilland flows, under decreasing temperature and pressure, from one of said stages to the next, comprising an interstage partition extending downward from the uppermost section of said adjacent stages and terminating above said flowing distilland; a vapor impermeable flexible flap, the top of said flap being connected to the bottom of said partition, the bottom of said flap extending in the direction of the lower pressure stage of said adjacent stages, the bottom of said flap being freely movable and in contact with said flowing distilland, the weight of said flap being such that it requires a force applied against it in order to overcome the pressure differential between said adjacent stages so as to maintain said contact with said flowing distilland; means connected to the downstream face of said flap at its lower end to exert said force on said flap, wherein the upstream face of said flap is essentially planar, and wherein said force means maintains said upstream face of said flap in wiping contact with the top surface of said flowing distilland, so that said flap offers negligible resistance to distilland flow, yet maintains a pressure seal between said adjacent stages.

2. The device of claim 1 wherein said force means is a weight attached to the downstream face of said flap.

3. The device of claim 1 wherein said force means comprises spring means attached to the downstream face of said flap. 

2. The device of claim 1 wherein said force means is a weight attached to the downstream face of said flap.
 3. The device of claim 1 wherein said force means comprises spring means attached to the downstream face of said flap. 